low pass digital filters

30oct13

The mock spectrometer has a low pass
digital filter after the a/d, digital mixer section. The filters are
8x overlap filters that are symmetric about DC. The decimation can
be 2 through 1024. The coef's for a particular decimation:

are 16 bit fixed point numbers

there are 8xdecNum coefs in total

There are 4 files, each containing DecNum coef. These are
mirrored about DC to give the 8*decNum coef.

The filter types available are:

rectangle

hamming

hanning (this is the default that we use)

blackman

bartlett

The filters are generated with jeffs program
(pnet_mkdlpf_coeff).

IDL routines:

Some idl routines used with the dlpf
processing:

pdevklpf.pro - make coef for a decimation and optionally store
it on disc

pdevinplpf.pro - input coef for a given decimation from disc.

03oct13:plot filter shapes and aliased
power. dec=2..15

Plots were made of the filter shapes (in the time
and frequency domain) for decimations 2 through 15 using the filter
coefficients.
The plots show: